Development of the precise dilatometer and study of spin lattice coupling of doped (Y,Lu)MnO3

최성일 성균관대학교 일반대학원 2017 국내박사

Multiferroic refers to multifunctional materials that simultaneously possesses two or more ferroic orders like ferromagnetism, ferroelectricity, and /or ferroelasticity. Hexagonal ReMnO3 is one of multiferroic compounds, which have giant spin–lattice coupling at an antiferromagnetic transition temperature. Despite extensive studies over the past two decades, the origin and underlying microscopic mechanism of strong spin–lattice coupling remain very much elusive. In this study, I developed a precise capacitive dilatometer. I carried out the whole processes and finally I obtained Å level of resolution. Here I describe the whole developmet story; design, assembly, test, calibration, and calculation. Through the development of the dilatom11eter, I went through a lot of trial and error, which finally made me understand the principle, physics, and precise experiment. I try to address the multiferroic mechanism of Hexagonal manganites by measuring the thermal expansion of doped single crystals Y1−xLuxMnO3 where x = 0, 0.25, 0.5, 0.75, and 1.0 with my dilatometer. From these measurements, we confirm that there is a progressive change in the physical properties with doping. At the same time, all our samples exhibit clear anomalies at TN, even in the samples where x = 0.5 and 0.75. This is opposed to some earlier ideas, which suggests an unusual doping dependence of the anomaly. Our work reveals yet another interesting facet of the spin–lattice coupling issue in hexagonal RMnO3. Keywords : dilatometer, multiferroic, hexagonal ReMnO3, spin-lattice coupling

Cr-Mo-V-Ti 저합금강에서 Normalizing 열처리조건에 따른 석출물의 거동

김홍기 부산대학교 2017 국내석사

화력발전소 보일러용 Tube 2.25Cr-1Mo-V-Ti 소재에서 M23C6 석출물의 최적 Solution 조건을 Dilatometer를 이용하여 관찰하였다. M23C6 석출물 최적 Solution 조건을 찾기 위해 900-1100℃에서 0, 600sec, 1800sec 열처리하였고 OM 및 SEM. EBSD, TEM 분석을 통해서 석출물의 상동정 및 분율을 측정하였다. 그리고 Dilatometer Curve에서 Bs점을 이용하여 C의 Solution을 예측하여 M23C6의 최적 Solution 조건을 선정하였다. 실험결과 900,1000,1100℃ 1800sec 조건에서 석출물이 최적 Solution 조건으로 판단되었으며 각 온도조건에 따른 Austenite Grain Size의 조대화의 최소를 고려하여 1000℃에서 1800sec 조건이 Solution 최적조건으로 판단하였다.

저 탄소강의 역변태 중 초석 페라이트 내 탄소 재분배

조원태 연세대학교 대학원 2010 국내석사

철강에서 역변태는 전체 열처리 과정 중 시작 단계로서 온도를 올리는 과정에서 나타나는 변태과정이다. 역변태 연구는 높은 온도에서 일어나는 역변태 현상을 관찰하기 위해 역변태 중에 급냉하여 기계적 연마 후 현미경으로 관찰하거나 dilatometer를 이용한 간접적인 실험이 주를 이루었다. 최근 들어 High-Temperature Confocal Scanning Laser Microscope 가 개발 되어 역변태를 실시간으로 관찰할 수 있게 되면서 초기상이 페라이트와 펄라이트로 구성된 강의 역변태 중에 massive 변태가 일어난다는 사실이 밝혀졌다. 또한, 역변태의 massive 변태 개시 온도는 초석 페라이트 내부의 탄소 농도와 밀접한 관련이 있으므로 이를 이용하여 탄소 농도의 정량적인 분석이 가능할 것으로 예상되었다. 본 연구에서는 High-Temperature Confocal Scanning Laser Microscope로 역변태 중 massive 변태가 시작되는 온도를 관찰하였다. 이를 이용하여 저탄소강의 역변태 중 페라이트 내부의 탄소 농도를 측정할 수 있는 방법을 제시하고 이 방법의 타당성을 IF steel로 검증하였다. 검증한 방법을 적용하여 S10C / S20 / S45C의 세 강종을 가지고 실험을 진행한 결과 역변태 중 페라이트 내부로 탄소가 확산되어 페라이트 내에 탄소가 과포화 됨이 예상되었고 이를 WDS (Wave Dispersive Spectrometer)와 micro-Vickers hardness 실험으로 증명하였다. 이와 같은 결과는 일반적인 역변태 모델링에서 일정하다고 가정하는 페라이트 내부의 탄소 농도를 변화하는 함수로 넣어야 더욱 정확한 예측 값을 얻9을 수 있음을 알려준다. 또한 S20C를 가지고 dilatometer 실험을 진행하여 High-Temperature Confocal Scanning Laser Microscope로 실험한 값과 비교하였다. 그 결과 dilatometer 결과값 만으로도 massive 변태 현상이 일어났음을 예측할 수 있었다.

Dilatometric analysis of magnetic transition and austenite formation in pure iron and low carbon steels

박지혜 Graduate School, Yonsei University 2015 국내박사

In this thesis, an advanced method for measuring the Curie temperature (TC) and heat capacity for the magnetic transition by using a dilatometer equipped with an induction heating system was suggested. The amount of heat absorption required for the magnetic transition was quantitatively analyzed and verified by comparing the measured values of the 3d ferromagnetic metals.The radio frequency (RF) oscillating field applied during dilatometric test can influence the strain change during magnetic transition. The strain change near TC was investigated during continuous heating and cooling of pure iron using different types of dilatometers. The abnormal expansion appeared near TC when the iron was heated using the dilatometer under the RF field, which was caused primarily by the change in electron-phonon interaction under the RF field. The effect of electron-phonon interaction was confirmed from that the thermal expansion coefficient in paramagnetic state, which is known to be greatly affected by the electron-phonon interaction, was proportional to the strength of the RF field.When pure iron is further heated above TC, bcc ferrite transforms to fcc austenite resulting in the strain decreases due to the difference in density between ferrite and austenite. Interestingly, the amount of strain contraction, measured by using a dilatometer during continuous heating, was extremely varied according to the heating rate. It has been known that an extraordinary change in strain can be caused by additional plastic deformation even under a very weak stress lower than the yield stress, which is called the TRansformation Induced Plasticity (TRIP) phenomenon. The effect of TRIP phenomenon was investigated by applying compressive stresses during dilatometric tests, and it was confirmed that the additional strain contraction can be occurred by the TRIP behavior. Because the RF field plays a crucial role in abnormal expansion near TC, it can also give rise to an anomalous strain change during austenitization. The effect of RF field on the abnormal expansion during ferrite to austenite transformation at high heating rate was confirmed by measuring the strain change by switching on/off the RF field at a constant cooling rate.The effect of grain morphology on the ferrite to austenite transformation was investigated by means of dilatometry. While the transformation rate of polygonal ferrite smoothly increases and decreases again during continuous heating, there were several peaks on the transformation rate for massive ferrite because the kinetics of austenite nucleation at irregular grain boundary and intragranular defects is different from the one nucleated at polygonal grain boundary.While the ferrite to austenite transformation occurs by the interface-controlled mechanism, the austenite formation in ferrite-pearlite mixed initial microstructure occurs by long-range diffusion of carbon. The ferrite-pearlite to austenite transformation in low carbon steel occurs by diffusive transformation at slow heating rate of 1 K/s, but occurs by a combination of diffusive and massive mechanisms at fast heating rates of 10 K/s and 100 K/s. During heating at 1 K/s, austenite transformed from different nucleation sites have different carbon concentration, resulting in inhomogeneous austenite microstructure.Meanwhile, at heating rates of 10 K/s and 100 K/s, the abnormal expansion due to the RF field was observed near TC at which the pearlite to austenite transformation is started. In these heating rates, formation of inhomogeneous austenite is more severe than the one at 1 K/s, which is caused by carbon-depleted austenite formed at ferrite grain boundaries and austenite massively transformed without carbon diffusion. The homogenization of austenite was completed at temperature approximately 180 K higher than the AC3 temperature. Therefore, it was found that the heating rate is crucial for measuring start and finish temperatures of formation of homogeneous austenite.

Fe-9Mn-6Al-0.15C 경량강의 연속 가열 및 등온 시효 중 κ-탄화물 석출 거동

정준영 연세대학교 대학원 2013 국내석사

Precipitation behaviors of κ-carbide during continuous heating and isothermal aging were studied in Fe-9Mn-6Al-0.15C (wt.%) lightweight steel, which has not been investigated, yet. κ-carbide precipitation and dissolution temperatures were measured during continuous heating at a heating rate of 0.1 oC/s by using high temperature differential scanning calorimetry (HT-DSC) and dilatometer. Two exothermic peaks appeared at 201 oC and 657 oC in DSC curve, and two volume expansions associated with phase transformation occurred at 216 oC and 619 oC. In the microstructure heated up to 300 oC, lath-type precipitates with a width of 5 ? 10 nm were observed within α′-martensite. It is turned out that the lath-type precipitates were κ′-carbides, which are metastable phase of κ-carbide, by using high-resolution transmission electron microscopy (HR-TEM) and energy dispersive spectroscopy (EDXS). During heating up to 550 oC, the lath-type κ′-carbide disappeared, and particle-type κ′-carbides were precipitated along δ-ferrite grain boundaries. During heating up to 700 oC, it is confirmed that both lath-type κ′-carbide and particle-type κ′-carbide were not observed. Through HR-TEM, X-ray diffraction (XRD) patterns, and literature reviews, lattice parameter and iron atomic volume of each phase were calculated, and then the dilatometric curves were analyzed considering the observed microstructure. Also, the dissolution of particle-type κ′-carbide was analyzed with two step mechanism including order-disorder transition. Before isothermal aging, the hot-rolled specimens were annealed at 820 oC for 10 minutes to maximize volume fraction of austenite, which transformed to κ-carbide during aging. After aging at 550 oC for 1h, it was observed that the particle-type κ-carbides were precipitated along δ-ferrite grain boundaries. After aging for 6h, the κ-carbides were precipitated forming lamellar structure. With increasing aging time, the volume fraction of κ-carbide was increased. The κ-carbide existed with lamellar structure have Nishiyama-Wasserman (N-W) orientation relationship. In the XRD results, there was no κ-carbide peak, but it is observed that austenite peaks were separated to solute-depleted austenite (γ0). Compensating for the loss of the volume fraction of austenite, the volume fraction of ferrite was increased with increasing aging time.

딜라토미터 시험을 이용한 인천국제공항부지 점성토의 지반공학적 특성

전창대 仁川大學校 一般大學院 2001 국내석사

최근 들어 흙의 지반공학적 특성을 추정하기 위한 콘 관입시험, 공내재하시험등의 현장시험이 국내에 도입되고 있다. 그러나 이런 시험들을 통하여 국내 연약지반의 지반공학적 특성을 추정하는 연구가 아직은 다소 미흡한 실정이며 또한 연약지반이 포함된 현장에서는 신속한 토질시험결과를 요구하고 있다. 본 논문은 인천국제공항 점성토 지반에서 딜라토미터 시험을 이용한 지반 공학적 특성에 대한 연구결과이며 딜라토미터 시험의 신뢰성을 평가해보기 위하여 피죠콘 관입시험, 채취된 불료란 시료의 물성시험 및 비압밀비배수 삼축압축시험등과의 결과를 토대로 딜라토미터 시험결과와 비교 분석하였다. 딜라토미터 시험을 분석한 결과, 실내시험 결과의 흙의 분류 및 단위중량과는 비교적 잘 일치하였으나 단위중량은 실내시험결과보다 다소 과소평가되고 있으며, Marchetti(1980)가 제안한 경험식으로부터 추정된 OCR 값은 실내시험에서 구한 OCR값 보다 다소 크게 나타나고, 딜라토미터 시험으로 추정한 비배수 전단강도와 피죠콘 관입시험으로부터 추정된 비배수 전단강도는 대체로 유사한 결과를 나타내었다. 최종적으로, 시험결과에 대한 분석을 시도하여 딜라토미터 시험과 정지토압 및 과압밀비와의 관계를 구한 결과 영종도 점성토의 정지토압계수에서는 소성지수(I_p)와의 경험식을 K_o = 0.71 + 0.0114(I_p), 과압밀비에서는 실내시험과 현장시험간에 OCR(_Lab) = 0.4855e^(0.5927x), (x=OCR_(DMT))의 새로운 경험식을 제안하였다. Site characterization is one of the most important performances in projects with regard to solve geotechnical problems. Dilatometer(DMT) test is a fast, economic, and accurate method of site characterization. However, the research to evaluate soil properties from this in-situ test is not sufficient in Korean soil. Field tests of the Dilatometer were performed to evaluate the existing correlations between Marchetti Dilatometer test(DMT) results and conventional soil parameters for marine soft ground in Inchon International Airport, As a reference test to compare with the DMT results, standard penetration tests and piezocone test, and a series of laboratory soil tests were performed. As a results, soil type, constrained modulus, coefficient of lateral earth pressure at rest, undrained shear strength, overconsoldation ratio were estimated from the Dilatometer tests. The methods used to obtain the soil parameters are mainly based on empirical correlations instead of theory. The soil parameters obtained from the Dilatometer tests are fairly well agreed with the results of the reference tests. From the analysis of the Dilatometer tests, empirical equations for determination of K_o is proposed as a function of I_p.

현장시험에 의한 사질토 고결영향 평가

이문주 고려대학교 대학원 2009 국내박사

Cementation of soil is a chemical mechanism of contacting bonds between particles, formed by the precipitation of bonding materials from solution. Cementation causes the increase in peak strength and the stiffness of soil, and it increases the penetration resistance on in-situ tests. Although there are many attempts for detecting and estimating the cemented sediment using in-situ tests, the complexity of behavior of cemented sand has contributed to the difficulty on interpretation of in-situ test results. For interpreting effect of cementation on behavior of sand, a cross-correlation of multiple measurements from different tests has been proposed as one of preferential methods. Therefore, this research focuses on the estimation of cementation effect of sand by analyzing results obtained from various measurements of in situ tests. For this purpose, miniature cone penetration tests, dilatometer tests and bender element tests were conducted on cemented specimen using large calibration chamber. In addition, in order to complement chamber test, a series of drained triaxial shear tests, unconfined compression tests and one dimensional compression tests were also performed. Because an extraction of natural homogeneous cemented sand without damage of cementation bonds is very difficult, cemented sand with gypsum was artificially prepared with changing content of gypsum and relative density. Based on results from a series of drained triaxial tests, an idealized concept is suggested to define the shear strength of cemented sand in three distinctive zones: the cementation control zone with a constant cohesion intercept at a low confining stress level, the transition zone in which the cohesion intercept is gradually reduced after a breaking point, and the stress control zone with almost zero cohesion intercept due to breakage of cementation bonds at a high confining stress level. The prediction equations for the shear strength and cohesion intercept in the cementation control zone and the transition zone are suggested from the analytical and experimental interpretation, and are verified from the experimental results. From calibration chamber tests, it is observed that the cone resistance (qc), dilatometer indices (KD, ED, ID), small strain shear modulus (Gmax), and constrained modulus (M) of sand increase with increasing gypsum content, but to different degrees. Analysis of test results shows that the cone resistance and dilatometer indices don?t represent properly the cementation effect of sand due to the damage of cementation bonds induced during penetration into the ground, however, the small strain stiffness of soil is most sensitive to cementation. The procedure of evaluating the deformation modulus from the cone resistance and dilatometer modulus underestimate the constrained modulus of cemented sand by about 70~85% and 25~70%, respectively. Experimental results show that M/ED ratio of cemented sand is significantly larger than that of uncemented one at same cone resistance, and unique M/ED?qc/pa relation is established regardless of cementation level. Because the Gmax is the more sensitive to cementation than penetration resistance or constrained modulus, values of Gmax/qc, Gmax/MD and Gmax/M of sand increase with cementation level. It is also estimated that Gmax of cemented sand in log scale linearly relates to the qc/ED ratio, and Gmax/qc of cemented sand is proportionally related to M/ED.

Evaluation of geotechnical properties of Busan newport clay

홍성진 Graduate School, Korea University 2011 국내박사

Adequate evaluation of geotechnical properties and ground improvement of soft ground are important to design and construct the geotechnical structures on soft soils. This study is concerned with the evaluation of geotechnical properties and ground improvement of Busan Newport clay. This paper is comprised of 3 topics, and the abstracts of 3 topics are as follows. A series of in-situ and laboratory tests were performed for the clayey soils of Busan area in order to develop the empirical correlations to evaluate the strength and compressibility of clay using CPT and DMT. The cone factors and correlation factors are obtained by comparing geotechnical properties with results of CPT and DMT, and these are compared with the soil properties representing the soil characteristics to develop the empirical correlations considering the soil characteristics. From the analysis of CPT results, it is observed that the cone factors (Nkt and Nke) are inversely proportional to the pore-pressure ratio. And correlation factors between the cone resistance and constrained modulus (αm and αn) and between the cone resistance and small strain shear modulus (αG) are observed to decrease with increasing plasticity index. From the analysis of DMT results, it is observed that the cone factor (Nc) is linear proportional to the material index (ID). And correlation factors between the dilatometer modulus and constrained modulus (RM) and between the dilatometer modulus and small strain shear modulus (R G) are observed to increases with 1/ID. Using these relationships various empirical correlations for Busan clay are developed. The compression index, which represents the compressibility of clay, is generally obtained from the consolidation test, or it has been predicted by the empirical correlations with typical soil properties. In this study, the results of consolidation tests on natural and remolded Busan and Inchon clays are analyzed to figure out the sedimentation state and its effect on the empirical correlations. Results of analysis show that the void index of Busan clay is higher than SCL while the void index of Inchon clay is lower than SCL. By comparing prediction errors with Δer, which represents the sedimentation state of clay, it is observed that errors predicting the compressibility based on the liquid limit and plasticity index decrease as Δer increases. Supplemented correlations predicting the compression index of Busan and Inchon clays are suggested using these relationships. In this study, a method, evaluating the compression index of natural clay from typical soil properties, is developed theoretically using the characteristics of remolded clay. By analyzing the consolidation test results of Busan and Inchon clays, the proposed method is verified. The proposed method evaluates the compression index of Busan and Inchon clays more accurately than compression index equations using a single soil parameter. The prediction errors are occurred by assumption, and prediction errors are inversely proportional to ecross/e0, generally. The permeability of adjacent soil to vertical drain has a decisive effect on the rate of consolidation by vertical drains due to the characteristics of radial flow. Therefore, the permeability of smear zone controls the rate of consolidation by vertical drains. In this study, a method is suggested to analyze the radial consolidation on the basis of consolidation characteristics of remolded clay. And the consolidation by PVDs of Newport site was analyzed to verify the suggested method. Because, the suggested method is not much affected by kh/ks, it can perform reliable analysis for consolidation by vertical drains. The comparison analysis results and field measuring data shows that the suggested method well predicts the rate of consolidation of Busan Newport, and appropriate extent of smear zone is calculated as 3~4dw by back-analysis, roughly. And in this study, a new approach evaluating the extent of smear zone from the measured settlement and void ratio reduction by disturbance is proposed, and the extent of smear zone of Busan Newport is calculated using this approach. The calculated rs.eq turns out to be from 2.6rw to 7rw, and the calculated rs.eq/rw is in accord with the back-analysis result of Newport site that ds/dw is about 3~4.

Development of the precise dilatometer and study of spin lattice coupling of doped (Y,Lu)MnO3

Choi, Seongil Sungkyunkwan university 2017 국내박사

산화주석/그래핀 나노 복합체 합성 및 리튬이차전지 음극소재용 전기화학적 특성 연구

김유석 연세대학교 대학원 2012 국내석사